Observational Constraints on the Regularized 4D Einstein-Gauss-Bonnet Theory of Gravity

TL;DR

This paper investigates observational constraints on the coupling parameter of the regularized 4D Einstein-Gauss-Bonnet gravity, finding tight bounds from satellite, black hole, and cosmological data that limit deviations from general relativity.

Contribution

It provides the first comprehensive analysis of observational bounds on the coupling parameter of the regularized 4D Einstein-Gauss-Bonnet gravity using multiple physical systems.

Findings

LAGEOS satellites constrain |α̂| ≲ 10^{10} m^2

Early universe and black hole observations limit α̂ to 0–10^8 m^2

Large deviations from GR are unlikely in most astrophysical systems

Abstract

In this paper we study the observational constraints that can be imposed on the coupling parameter, $\hat \alpha$, of the regularized version of the 4-dimensional Einstein-Gauss-Bonnet theory of gravity. We use the scalar-tensor field equations of this theory to perform a thorough investigation of its slow-motion and weak-field limit, and apply our results to observations of a wide array of physical systems that admit such a description. We find that the LAGEOS satellites are the most constraining, requiring $| \hat \alpha | \lesssim 10^{10} \,{\rm m}^2$. This constraint suggests that the possibility of large deviations from general relativity is small in all systems except the very early universe ($t<10^{-3}\, {\rm s}$), or the immediate vicinity of stellar-mass black holes ($M\lesssim100\, M_{\odot}$). We then consider constraints that can be imposed on this theory from cosmology, black hole systems, and table-top experiments. It is found that early universe inflation prohibits all but the smallest negative values of $\hat \alpha$, while observations of binary black hole systems are likely to offer the tightest constraints on positive values, leading to overall bounds $0 \lesssim \hat \alpha \lesssim 10^8 \, {\rm m}^2$.